1. Field of the Invention
The present invention relates to separation of plasma from whole blood. Particularly, the present invention relates to a medical device capable of separating plasma from agglutinated blood cells through a porous filter membrane.
2. Description of Related Art
Plasma is the liquid portion of blood primarily comprised of water. The water portion of the plasma is freely transferable with cells of the body and other extra cellular fluids. Plasma is also comprised of salts, glucose, amino acids, vitamins, hormones and metabolic waste products. As a whole, plasma provides the means to suspend white blood cells, red blood cells and other cellular components for transfer through a human or animal. If a plasma sample is desired, separation from the other cellular components of blood must occur well before coagulation of the blood. Once the blood coagulates, serum is the remaining liquid portion of the collected blood sample, which is devoid of some protein components of blood.
Because plasma contains a rich source of components available for diagnostic analysis, medical devices are available for use in separating plasma from a whole blood sample. Several prior art examples provide evacuated multi-chamber devices, which incorporate a filter used to yield plasma removed from a collected blood sample. In some of the prior art examples, the devices use a detachable chamber, allowing a user to access the separated plasma specimen. In addition, the prior art devices typically use a filter membrane having small and fine pore sizes to prevent cellular components from passing therethrough, which can render the vacuum forces generated by the evacuated device inadequate to drawn plasma from a collected blood sample.
Ishimito et al. disclose a blood separating tube in U.S. Pat. No. 6,506,167 entitled, “Blood-Collecting Tubes,” including an upstream tube separated by a filter from a downstream tube where the tubes are attachable to and detachable from each other and are evacuated. During blood collection, blood is removed from a patient through intravenous puncture and transferred into the upstream tube through blood pressure and negative pressure inside the tube. In accord with the disclosure, a pressure differential is supposed to be created between the upstream tube and the downstream tube as the blood contacts the filter between the two tubes. Several suggested filters include a membrane, glass fibers, filter paper with large pores having attached thereto anti-hemocyte antibodies, a filter impregnated with a cationic macromolecular substance to aggregate cells, and a laminated multi-layer filter. Problems that exist with this disclosure are blood cells clogging the filter and an inadequate vacuum force between the upstream tube and downstream tube during blood collection. A further problem that exists with this disclosure is exposing any plasma collected in the downstream tube to contaminants should the downstream tube be removed from the upstream tube.
Konrad, in United States Patent Application Publication No. 2003/0013205, entitled “Separating Device,” describes a preferred method of producing a concentration of nucleic acids, RNA or DNA, from whole blood by way of a liquid-permeable separating element. The separating elements disclosed include filters, silicate membranes, ion-exchange membranes and columns or separating columns. It is disclosed that the invention is capable of causing the release of nucleic acid molecules from the cellular components of the blood through lysis. The collected sample containing lysed blood cells is passed through a separating element, which is capable of adsorbing the nucleic acid component. The separating element can be removed for later molecular diagnostic analysis. Konrad does not disclose plasma separation from whole blood.
Murto et al., in World Intellectual Property Organization International Publication No. WO 02/29406 entitled “Methods and Devices for Processing Blood Samples,” describes methods and related devices and reagents for separating plasma from a whole blood sample. The invention as disclosed describes a method of separating plasma from the cellular components of whole blood by mixing a reagent comprising magnetically attractable particles having an agglutinating agent bound thereto with a whole blood sample. The purpose of the magnetic reagent is to bind the cellular components of the whole blood sample. A magnetic force is then applied to the mixture to separate the magnetic reagent with cells bound thereto from the plasma. The plasma is separated from the mixture by pipetting, decanting, siphoning or wicking.
There is a present need for a device that is capable of providing sufficient force by the internal vacuum force of the tubes to separate agglutinated blood cells from plasma without clogging of the filter, and which is easy to use in clinical and research applications while providing an uncontaminated plasma specimen.